The present invention relates to microelectromechanical system (MEMS) devices, and more particularly to elevating structures that allow for MEMS devices to be spatially positioned in diverse orientations with respect to the microelectronic substrate.
Advances in thin film technology have enabled the development of sophisticated integrated circuits. This advanced semiconductor technology has also been leveraged to create MEMS (Micro Electro Mechanical System) structures. MEMS structures are typically capable of motion or applying force. Many different varieties of MEMS devices have been created, including microsensors, microgears, micromotors, and other microengineered devices. MEMS devices are being developed for a wide variety of applications because they provide the advantages of low cost, high reliability and extremely small size.
Design freedom afforded to engineers of MEMS devices has led to the development of various techniques and structures for providing the force necessary to cause the desired motion within microstructures. For example, microcantilevers have been used to apply rotational mechanical force to rotate micromachined springs and gears. Electromagnetic fields have been used to drive micromotors. Piezoelectric forces have also been successfully been used to controllably move micromachined structures. Controlled thermal expansion of actuators or other MEMS components has been used to create forces for driving microdevices. One such device is found in U.S. Pat. No. 5,475,318 entitled xe2x80x9cMicroprobexe2x80x9d issued Dec. 12, 1995 in the name of inventors Marcus et al., which leverages thermal expansion to move a microdevice. A micro cantilever is constructed from materials having different thermal coefficients of expansion. When heated, the bimorph layers arch differently, causing the micro cantilever to move accordingly. A similar mechanism is used to activate a micromachined thermal switch as described in U.S. Pat. No. 5,463,233 entitled xe2x80x9cMicromachined Thermal Switchxe2x80x9d issued Oct. 31, 1995 in the name of inventor Norling.
Electrostatic forces have also been used to move structures. Traditional electrostatic devices were constructed from laminated films cut from plastic or mylar materials. A flexible electrode was attached to the film, and another electrode was affixed to a base structure. Electrically energizing the respective electrodes created an electrostatic force attracting the electrodes to each other or repelling them from each other. A representative example of these devices is found in U.S. Pat. No. 4,266,339 entitled xe2x80x9cMethod for Making Rolling Electrode for Electrostatic Devicexe2x80x9d issued May 12, 1981 in the name of inventor Kalt. These devices work well for typical motive applications, but these devices cannot be constructed in dimensions suitable for miniaturized integrated circuits, biomedical applications, or MEMS structures.
In conventional MEMS devices, such as thermal bimorphs and flexible electrostatic actuators, the devices have been directly attached to the underlying microelectronic substrate. Such direct attachment limits the orientation of the resulting motion or force and limits the complexity of devices that can be deposited on any one substrate. Recent improvements in MEMS devices have led to more robust structures, capable of imparting greater force and greater degrees of actuation. In many applications numerous MEMS devices have been fabricated in array-like fashion on the microelectronic substrate to further leverage these improvements. However, in instances where the MEMS devices are attached directly to the substrate the complexity of the array formation is limited to the available area on the surface of the substrate.
To alleviate this problem what is desired is a structure that can serve to elevate the point of attachment above the surface of the substrate. Such an innovation would allow the point of attachment to exist in any plane of orientation in respect to the underlying substrate. In this regard, the corresponding MEMS devices that are attached at these elevated points of attachment can impart force and motion in a myriad of directions. By providing for the capability to raise the point of attachment above the substrate MEMS optical attenuators can be developed that allow for optical beam deflection proximate the substrate while maintaining ample spacing between the optical beam and the substrate. In this manner, light tables could be created with the path of the beam determined by multiple actuators capable of deflecting beam in a full three-dimensional range of paths.
Additionally, it would be highly beneficial to provide for an elevating structure that allows for multiple MEMS devices to be attached to any one elevating structure. This arrangement would allow for a higher area concentration of MEMS devices on a substrate, thus, imparting greater force and movement. In application, an increased device concentration would benefit MEMS pumps where improved flow rates could be realized. Device concentration could also be realized by fabricating systems having both elevating structures with attached MEMS devices and underlying MEMS devices attached directly to the substrate.
Further benefit can be gained by developing an elevating structure that not only raises MEMS device lines of attachment above the substrate but also provides for motion capabilities in and of itself. In this instance the elevating structure serves to impart dual actuation and/or force. The MEMS device can impart force or movement in one direction and the elevating structure can impart force or movement in another direction. This allows for the MEMS device to operate in variable planes depending on the orientation of the elevating structure.
As such, a need exists to provide for a MEMS elevating structure having corresponding attached MEMS devices spatially oriented in diverse planes above the underlying microelectronic substrate. This benefit can be realized in providing for MEMS forces and displacements in innumerable orientations and increasing MEMS device concentration on a given substrate. These benefits are particularly attractive to current MEMS devices that impart greater force, movement and overall precision. Many MEMS devices, such as attenuators, switches and pumps will benefit from having the diverse orientations, higher device concentration and variable planes of operation.
Microelectromechanical system (MEMS) apparatus are therefore provided that are capable of elevating the attachment point of MEMS devices in a plane remote from the underlying microelectronic substrate. Additionally, the MEMS apparatus provide the capability to spatially position the attached MEMS devices in diverse planes of orientation and to concentrate MEMS devices across the underlying microelectronic substrate.
The MEMS apparatus includes a microelectronic substrate and an elevating structure having a fixed portion attached to the substrate and a distal portion raised from the surface of the substrate. The distal portion of the elevating structure defines at least one zone of attachment. Additionally, the MEMS apparatus comprises a MEMS device attached to the distal portion of the elevating structure at one of the zones of attachment.
In one embodiment of the invention the attached MEMS device comprises an electrostatic actuator having first and second electrode films that are attached to the elevating structure at one of the zones of attachment. The MEMS electrostatic actuator may comprise one generally rigid film and one generally flexible film or the actuator may comprise two generally flexible films. In the embodiment in which the actuator comprises one generally rigid film and one generally flexible film, the flexible film can be biased to curl away from or towards the generally rigid film absent electrostatic forces. In the embodiment in which the actuator comprises two generally flexible films, the films can be biased to curl in the same or opposite direction. In other embodiments of the invention other MEMS devices, such as MEMS thermal bimorphs, may be attached to the elevating structure at one of the zones of attachment.
In those embodiments in which the MEMS devices comprise an electrostatic actuator the force and movement provided by the actuator may be used to incorporate switches, pumps, valves or other similar MEMS devices. In one embodiment the electrostatic actuator may comprise an optical attenuator. In such an embodiment, the flexible film(s) may include reflective surfaces that are capable of deflecting optical beams. In this fashion, the underlying substrate can serve as an optical table capable of directing the path of various optical beams that lie in planes proximate to the substrate.
The geometric configuration of the elevating structure will dictate the number of zones of attachment, as well as, the orientation of the planes that the attached MEMS devices will occupy. In a simplified embodiment the elevating structure defines one zone of attachment that is generally parallel to the underlying microelectronic substrate. In another embodiment of the invention, the distal portion of the elevating structure extends upward so that a generally flat segment lies perpendicular to the surface of the substrate. In one embodiment, the generally flat portion defines three zones of attachment that allow for MEMS devices to be attached to the elevating structure at planes of orientation generally perpendicular to the substrate. In another embodiment, the generally flat portion defines two zones of attachment that allow MEMS devices to be attached to the elevating structure at planes of orientation generally perpendicular to the substrate. In embodiments having more than one zone of attachment, MEMS devices can be attached to one or more of the zones.
In one embodiment of the invention the elevating structure is a passive device that remains relatively stationary upon release from the substrate. In another embodiment, the elevating structure is an active structure that can be electrostatically actuated via an electrode disposed in the elevating structure and an electrode deposited on the microelectronic substrate.
The invention is further embodied in an array of MEMS apparatus disposed on the surface of a microelectronic substrate. The array comprising more than one elevating structure disposed on the surface of the substrate in a predetermined pattern. Each elevating structure has a fixed portion attached to the substrate and a distal portion raised from the substrate that defines at least one zone of attachment. Additionally, each elevating structure has at least one MEMS device attached to the distal portion of each of the elevating structures at one of the predetermined zones of attachment. The MEMS devices attached to the elevating structures may comprise electrostatic actuators or other compatible MEMS devices.
The MEMS apparatus of the present invention allow for MEMS devices to be spatially oriented in diverse planes above the underlying microelectronic substrate. The benefit of this alignment can be realized in providing for MEMS forces and displacements in innumerable orientations. Additionally, by providing for placement of MEMS structures above the underlying substrate a higher concentration of MEMS devices can exist on a given substrate. Many MEMS devices, such as attenuators, switches and pumps will benefit from having diverse orientations, higher device concentration and variable planes of operation.